Circuit interrupters such as circuit breakers are one of a variety of overcurrent protection devices used for circuit protection and isolation. The circuit breaker provides electrical protection whenever an electric abnormality occurs. In a typical circuit breaker, current enters the system from a power line and passes through a line conductor to a stationary contact fixed on the line conductor, then to a movable contact. The movable contact is fixedly attached to a pivoting arm. Arc chutes can be used to direct an arc away from the electrical contacts into the arc chute. The arc chute is situated proximate to the stationary contact of the circuit. As long as the stationary and movable contacts are in physical contact, current passes between the stationary contact and the movable contact and out of the circuit breaker to down-line electrical devices.
In the event of an overcurrent condition (e.g., a short circuit), extremely high electromagnetic forces can be generated. The electromagnetic forces can be used to separate the movable contact from the stationary contact. Upon separation of the contacts and blowing open the circuit, an arcing condition occurs. The breaker's trip unit will trip the breaker which will cause the contacts to separate. Also, arcing can occur during normal “ON/OFF” operations of the breaker.
Circuit breakers typically have one of two types of arc extinguishing apparatus. In miniature circuit breakers, typically used in residential and light commercial installations, the contacts are enclosed in a chamber in the resin casing and partially surrounded by a metal shield as shown for example by U.S. Pat. No. 4,081,852, the content of which is hereby incorporated by reference as if recited in full herein. In larger circuit breakers such as that described in U.S. Pat. No. 4,866,226, arc extinguishers typically comprise a plurality of stacked, substantially U-shaped arc extinguishing plates which surround the fixed and movable contacts of the circuit breaker. The content of this patent is hereby incorporated by reference as if recited in full herein. Various materials have been used for the arc chute and for the molded housing of the circuit breaker. See, U.S. Pat. No. 5,359,174, the content of which is hereby incorporated by reference as if recited in full herein.
For example, the arc chute can be held by molded housing walls of suitable material of a molded case circuit breaker. Arc-extinguisher side walls have in the past been formed of fibers within a melamine resin matrix, as disclosed in U.S. Pat. No. 4,950,852. Such resins are used to provide a source of arc-quenching gaseous molecular compounds released based on the heat of the arc. U.S. Pat. No. 4,975,551 discloses an arc extinguishing composition comprising an arc-interrupting compound, such as melamine, which is disposed along the path of the arc in combination with a binder composition. U.S. Pat. No. 3,761,660 discloses an arc interrupting composition of alumina and melamine for the arc-exposure walls or surfaces of electric circuit interrupting devices. The patents in this paragraph are incorporated by reference as if recited in full herein.
Despite the above, there remains a need for cost-effective molded case circuit breakers that can meet UL® 489 requirements. As is known to those of skill in the art, UL® 489 requires that these circuit breakers meet specific construction and testing requirements to provide necessary protection while requiring little or no maintenance. These types of circuit breakers have an enclosed molded case which provides personal safety as well as proper dielectric clearances. The scope of the UL® 489 standard for molded case circuit breakers includes miniature circuit breakers, molded case circuit breakers and insulated case circuit breakers. These circuit breakers are typically rated 10-6000 A and up to 600 Vac and 500 Vdc.